Boost converters are commonly used in high power factor applications as line conditioners. The boost stage processes the AC input and develops a DC output voltage, typically 400 V or 800 V. Boost converters are typically the topology of choice for providing a high output voltage (i.e., 400 V or 800 V) from substantially lower input DC voltages derived from sinusoidal input voltages. In applications with high AC input voltage (i.e., 320 to 480 VAC) where an intermediate DC bus voltage of 700 to 800 V is necessary, a soft-switched boost is often used to maintain the overall efficiency of the rectifier. For lower AC input voltage applications, a simple snubber to slow down the turn-off of the boost diode is all that is necessary to obtain a boost efficiency of 96-98%. In recent years, several new topologies have been proposed in which the semiconductor switching losses arc minimized by adding an auxiliary active circuit. The addition of the auxiliary circuit is an elegant solution but it results in increased cost and complexity.
A recent paper by Y. Jiang and F. C. Lee, entitled "Three-Level Boost Converter for Application in Single Phase Power Factor Correction", Virginia Power Electronics Center (VPEC) Power Electronics Seminar Proceedings, 1994, Virginia Polytechnic Institute and State University, Blacksburg, Va., pp. 127-133 suggests a configuration for a boost stage that accommodates semiconductor devices rated for approximately half the normal output voltage, (i.e., V.sub.0 /2) for use in high voltage, single-phase applications. Jiang and Lee's circuit, which they call a three-level boost, provides two unparallelable but equal output voltages. By reducing the maximum voltage stresses across the semiconductor devices, a zero-voltage switching topology becomes less important to maintain high efficiency. In addition to reducing the voltage stresses across all semiconductor devices to half of the normal output bus voltage, the three-level boost also decreases the size of the boost inductor without compromising EMI performance.